I recently posted data on the number of unique NIH PIs for all mechanisms listed in the NIH RePORT database.
I have now analyzed data for R01-equivalent grants (primarily R01s but also R23, R29, and R37 (MERIT) awards) as shown below:
This shows curves for all PIs (including multiple PIs) and for Contact PIs only. These curves clearly reveal the impact of the NIH budget "doubling" from FY1998 to 2003) and the subsequent decline due to the worse-than-flat NIH budget over the past 12 years (with the exception of the ARRA) funding.
The correction for multiple PIs is significant (although, of course, being PI on a multiple PI grant likely provides fewer resources than being the sole PI on an award of the same size). The 3564 New (Type 1) R01 grants in FY2014, 771 had multiple PIs.